The present invention relates to a carbon black, its preparation and its use.
Carbon blacks are used on a large scale as a black pigment and as a reinforcing agent and filler. They are produced with different properties by various processes. Most frequent is preparation by means of oxidative pyrolysis of carbon-containing carbon black raw materials. In that process, the carbon black raw materials are burnt incompletely at high temperatures in the presence of oxygen. This class of carbon black preparation processes includes, for example, the furnace black process, the gas black process and the lamp black process. The carbon-containing carbon black raw materials used are predominantly polynuclear aromatic carbon black oils. The product stream of oxidative pyrolysis consists of a waste gas containing hydrogen and carbon monoxide and, suspended therein, finely divided carbon black, which is separated from the waste gas in a filtering installation.
In the furnace black process, incomplete combustion takes place in a reactor lined with highly refractory material. A stream of hot waste gases is produced in a pre-combustion chamber by burning a fuel/air mixture, and the carbon black raw material is sprayed or injected into that stream. The carbon black that forms is quenched by the spraying of water into the reactor and is separated from the stream of gas. The furnace carbon black process permits the preparation of carbon blacks having a very wide range of carbon black properties.
The lamp black apparatus consists of a cast-iron shell, which receives the liquid or, optionally, molten raw material, and a closed hood having a refractory lining. The air gap between the shell and the closed hood, as well as the low pressure in the system, serve to regulate the supply of air and hence to influence the properties of the carbon black. As a result of the heat radiation of the closed hood, the raw material vaporizes and is partly burnt but mainly converted into carbon black. In order to separate off the carbon black, the process gases containing carbon black are passed into a filter after cooling.
In the gas black process, the carbon black raw material is first vaporized into a hydrogen-containing carrier gas stream and then burnt in a plurality of small flames beneath a cooled roller. Some of the carbon black that forms is deposited on the roller and some is discharged with the process gases and removed in a filter.
The mentioned processes for preparing carbon black are known from Ullmanns Enzyklopadie der technischen Chemie 4. edition Volume 14 page 633 ff.
All three processes may in principle be used within the context of the invention, but preference is given to the furnace process.
It is known to dope carbon black with silicon. Carbon blacks doped with silicon are known, for example, from WO 96/37547. Silicon-containing carbon blacks can be prepared, for example, by adding silicon-containing compounds to the carbon black raw material.
It is further known to dope carbon black also with other elements (U.S. Pat. No. 3,448,052; EP 278 743 A1; EP 829 511 A1). The doping processes are similar to silicon doping.
Aggregates consisting of a carbon black phase and a metal-containing phase are known from WO 98/42778.
Also known is a process for the preparation of an intimate mixture of carbon black with oxides of the elements boron, silicon, aluminum, titanium, zirconium, zinc, lead, tin, iron, cobalt, nickel, manganese, chromium, vanadium, molybdenum, niobium and tantalum (U.S. Pat. No. 3,094,428).
There is further known a process for the preparation of carbon black by introduction of a metal compound of the group gallium, indium, aluminum or mixtures thereof (U.S. Pat. No. 3,306,762). The addition of those metal compounds, like the addition of alkali metal compounds, brings about a lowering of the structure.
Also known is a process for the preparation of carbon blacks by addition of rare earths having atomic numbers from 57 to 71 (U.S. Pat. No. 3,383,175).
An object of the present invention is to make available a carbon black having special properties such as, for example, changed shade of color, changed electrical properties, changed pH value, functional groups, sites of reaction, and improved dynamic properties in rubber. A further object is to influence the structure of the carbon black.